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FIELDAYS PREVIEW Understanding energy in dairy nutrition I By ALUN FAULKNER N New Zealand, the energy of a ruminant diet is often defined as metabolisable energy per kilogram of dry matter (MJ ME/kg DM). This can be a misleading as high energy feeds are not necessarily best, as the term fails to identify what nutrients contribute to this energy and where this energy is utilised by the animal. In ruminant animals, 80 per cent of the energy is supplied by the rumen microbes converting complex carbohydrates in grass, hay or supplementary feeds into volatile fatty acids (acetic, propionic and butyric acid) via a fermentation process. These acids are absorbed into the bloodstream and together with oxygen supply energy for bodyweight gain, pregnancy, bodyweight maintenance, milk production and activity (walking). An often-quoted term is fermentable ME (FME), which tries to quantify the energy in the diet that is fermentable in the rumen. These complex carbohydrates are supplied in different forms and have different fermentation rates in the rumen: Fibre – this includes cellulose, hemicellulose and lignin and is present in roughages like grass, hay, silage and straw and the nutritive value is often stated by the neutral detergent fibre (NDF) values. The rumen microbes ferment cellulose to produce acetic acid which is important in production of milk fat. Due to the varying lignin component of cellulose, the rate of fermentation of cellulose is relatively slow compared to Alun Faulkner starch and sugars. The cellulose digesting microbes are very sensitive to fats and incorporation of high levels of fats in supplementary feeds can eliminate or slow down these microbes. It is therefore important that any supple- mentary fat is supplied as “rumen bypass fat”. Starch – this is present in cereal grains such as wheat, barley and maize and also in tropical root crops such as tapioca/cassava. The microbes that ferment starch are different to those that ferment cellulose and convert starch to propionic and lactic acid. Starch is present in grains at different levels and have different fermentation rates within the rumen. The table below shows that tapioca and wheat have rapid fermentation rates while maize and sorghum gave relatively lower fermentation rates. VISIT OUR SITE K18 AT THE NATIONAL FIELDAYS® MYSTERY CREEK On Site ONLY 'SPECIALS' Including 24 plant Bird or Shelter Packs $24.00 ea or 2 for $40.00 Plus 4 chances to WIN a box of Native Plants Enter the competition on site. Auckland & Taupo • P O Box 437 Taupo Phone: 07 378 5450 • Fax: 0800 828 764 Email: tauponativeplant@clear.net.nz Web: www.tauponativeplant.co.nz PRODUCT LAUNCH Walkease™ developed by Shoof. The affordable early intervention tool that should be in every Hoofcare tool box. FREE HOOFCARE WORKSHOPS Wed - Fri 10am - 3pm Local qualified Vets show how it should be done and answer all your questions. It is important to balance the starch sources in the feed with the forage to provide an ME with a balanced fermentation rate that utilises the effective rumen degradable protein (ERDP) present in grass. Sugar – this is present in grass and in products like molasses and sugar beet. The microbes ferment sugars into propionic and butyric acid which are a source of energy. Fats/oils – As stated above it is important that unsaturated fats are protected from breakdown in the rumen as their inclusion impairs the action of the rumen microbes. High inclusion of unprotected fats into dairy diets may improve the theoretical ME/kg DM of the diet but in practice can cause poorer function of the rumen and hence a poorer energy production from rumen microbes. Fats are a good source of energy but it is preferable that bypass or protected fats are used which bypass the rumen and so Cowslips Meet Karla, of Giltspur ™ (the Cowslips manufacturer) in Ireland. Call free 0800 800 801to find the store nearest you or visit our site at the 2009 National Fieldays, site F23 60 The Dairyman JUNE 2009